Copending application Ser. No. 09/041 068, owned by the Assignee hereof, illustrates therein a press arrangement which is particularly desirable for permitting molding of large plastic parts, such as urethane parts. The press arrangement of the aforesaid application incorporates ball-screw drive shaft arrangements for effecting relative opening and closing movement of the opposed mold bearing press platens. The drive arrangements of this press have proven highly desirable with respect to the performance they provide, and are particularly desirable where the press is mounted on a mobile carrier, such as an overhead support track, since the press does not have to rely on the use of hydraulic actuators and the like for the major performance functions carried out thereby. In the aforementioned press, the ball-screw drive actuators are controlled by both high speed and low speed drives which react with at least one of the press platens to provide rapid opening and closing movement of the press platen, and provide for slow movement throughout a small stroke which exists at the time the opposed mold parts are being moved into a closed relationship. This arrangement, in conjunction with the brakes associated with the drive motors for the screw shafts, provides the desired control over the press platens.
The press arrangement of the aforesaid application has proven highly desirable, but nevertheless in some situations the press is of a more sophisticated and complex construction than is necessary or desired.
In other known rim presses, the final closure of the mold has often been accomplished using fluid pressure devices such as air bags or the like. In these known presses, however, the final closure stroke has generally been large (i.e., three-fourths inch or greater), and this has imposed limitations with respect to adapting the press to different tool sizes, and limitations due to the required structure of the air bag and the required large quantity of pressurized air. This press construction also encourages users to insert spacers into the press to minimize the stroke and increase the closure force, but this can often cause damage to the tool (i.e., mold).
Accordingly it is an object of this invention to provide an improved press arrangement which, while it utilizes ball-screw drive units for providing rapid but desirable control over the primary opening and closing movement of the press, it in addition is provided with a pneumatic closure arrangement which provides the final small-stroke closing movement and holding force for the mold, whereby the overall press arrangement is mechanically simplified, and such press arrangement is equally usable either when mounted on a mobile overhead carrier or when provided in association with a stationary floor-supported frame.
In the improved press arrangement of this invention, the ball-screw drive arrangements are activated to permit rapid movement of one of the press platens (the upper press platen in the illustrated embodiment) during the basic opening and closing movements of the press. When substantially in a closed position, that is in a position which is closely adjacent but spaced from a fully closed position by only a very small distance, then full closure between the mold parts is effected by a mold displacing arrangement such as an air pressure lifting device associated with one of the press platens (the lower press platen in the illustrated embodiment) to effect full closure of the mold and holding of the mold in the closed position during the molding operation. The activation of the mold displacing arrangement also acts through the mold to cause the ball-screw drive arrangement to be axially displaced a small amount sufficient to cause automatic engagement of a friction brake which effectively nonrotatably holds the screw shaft to prevent back driving thereof due to the mold closure force, whereby separate latching of the upper press platen is not required. The friction brake automatically disengages when the mold closing force is released.
In the improved press arrangement of this invention, as aforesaid, the upper and lower press platens are preferably respectively provided with booking plates which mount the mold halves thereon, and which are each preferably supported in such fashion as to permit the booking plates to be pivotally moved so as to face sidewardly, preferably toward opposite sides of the press, to facilitate access to the mold halves mounted thereon. In the preferred and illustrated embodiment, the lower booking plate and the lower press platen in its entirety is vertically swingable through a limited extent about a horizontal pivot axis to permit sideward tilting of the lower press platen to facilitate access to the lower mold half.
The improved press arrangement of this invention, as aforesaid, also includes, as an option thereon, preferably on the lower press platen, a release mechanism which acts in opposition to the mold displacing arrangement so as to facilitate cracking (i.e., initial opening) of the mold in the event that deactivation of the mold displacing arrangement is inadequate to effect mold separation.
The improved press, as aforesaid, also permits a short-stroke, high-force closure of the mold by a pneumatic device which can be maintained of simple construction and function.